Worldwide demand for Internet bandwidth is growing rapidly each year, driven largely by video demand and the prevalence of mobile devices. Coherent transmission is a class of modulation technology that are commonly used for 100 G or faster dense wavelength division multiplexing (DWDM) optical networks. In coherent transmission, the transmitter modulates both phase and amplitude of the optical carrier. Coherent transmission is particularly well suited for long haul networks, where maximizing fiber capacity is an important consideration.